traditional chinese foods 2009 - li zaigui & tan hongzhuo

Chapter 1 by Li Zaigui and Bi Ying China Agricultural University, “Chinese steamed bread”, looked into the development of staple traditional food mantou Chinese Steamed Bread, CSB in: 1

T RADITIONAL C HINESE F OODS :

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F OOD S CIENCE AND T ECHNOLOGY S ERIES

Food Science and Technology: New Research

Lorenzo V Greco and Marco N Bruno (Editors)

2008 ISBN: 978-1-60456-715-1

The Price of Food

Meredith N Fisher (Editor)

2009 ISBN: 978-1-60692-440-2

Food Processing and Engineering Topics

Maria Elena Sosa-Morales and Jorge F Velez-Ruiz (Editors)

2009 ISBN: 978-1-60741-788-0

Traditional Chinese Foods: Production and Research Progress

Li Zaigui and Tan Hongzhuo

2009 ISBN 978-1-60692-902-5

TRADITIONAL CHINESE FOODS:

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L IBRARY OF C ONGRESS C ATALOGING - IN -P UBLICATION D ATA

C ONTENTS

P REFACE

It is generally admitted that the expression ‘traditional food’ refers to a product with specific raw materials, and/or with a recipe known for a long time, and/or with a specific process China has a wealth of traditional foods such asChinese steamed bread, Chinese noodles, Chinese rice noodles, Starch noodles (Vermicelli), Tofu, Sofu (soybean cheese), douchi (fermentation soybean), Chinese vinegar and many other foods These traditional foods are an important component of Chinese people’s diet and the basis for their food habits and nutrition They also constitute an essential aspect of their cultural heritage and related closely to Chinese people’s historical background and to the environment in which they live During the last few decades, the development of international food trade and the extensive urbanization process which have affected life-styles to a large extent in many parts of the world have resulted in a sizeable decrease in the consumption of some kinds of traditional foods and a relative neglect in the cultivation of traditional food crops Some traditional foods had withered away or are withering away The governing bodies of FAO have recommended that FAO give due consideration in its programme to the promotion of the production and consumption of traditional foods worldwide Several studies and projects have been initiated

by FAO and EU in different parts of the world to survey existing traditional foods and food crops, especially Chinese traditional foods Accordingly, China government, academia and industry all begin to give more attentions to own traditional foods, study their nutritional values and identify ways and means of promoting their production and consumption In recent years, as a result of food globalization, the consumption of traditional foods has increased considerably and many of these foods are concurrent with easy-to-prepare, processed, semi-processed and high-tech foods For example, tofu is sold in almost all of supermarket even in west countries It was decided therefore that a book should be carried out to document existing Chinese traditional foods in China and to assess their nutritional value and contribution to the diet

Among many new works on food, however, few studies address the Chinese foodways, despite their enormous and continual influence on local food habits around the world Even classic works on Chinese food provide us with only basic information about China itself, or interpret Chinese foodways in the restricted local food scene and within Chinese history This book however provides an up-to-date reference for traditional Chinese foods and a detailed background of history, quality assurance, and the manufacture of general traditional food products It contains topics not covered in similar books It is divided into 8 chapters We shall highlight the main point in each of the chapters, with emphasis on additional

background information that connects the individual chapters to others and to the overall theoretical concerns as well

Chapter 1 by Li Zaigui and Bi Ying (China Agricultural University), “Chinese steamed bread”, looked into the development of staple traditional food mantou (Chinese Steamed Bread, CSB) in: (1) The Definition, Categories and Consumption of CSB; (2) Materials for the production of CSB; (3) Situation and its development of processing technology for CSB making; (4) Researches on the requirements of flour quality for different kinds of CSB; (5) Methods which can improve CSB production including addition of different kinds of flour or additives; (6) Quality and properties of CSB

Chen Jie (Henan University of Technology) in Chapter 2, “Chinese noodles”, detailed (1) history and development of noodles; (2) Raw materials for noodles making; (3) Processing technology and equipments for different kinds of noodles such as fine dried noodles, instant noodles and long life noodles; (4) Researches on noodles processing

Liang Jianfen (China Agricultural University) in Chapter 3, “Chinese rice noodles”, brought follows information on rice noodles: (1) Origin, history and classifications of rice noodles; (2) Materials for rice noodle; (3) Processing procedures and (4) Quality evaluation

In Chapter 4, “Starch noodles (Vermicelli)”, Tan Hongzhuo (Academy of State Administration of Grain) summarized the current knowledge on: (1) Definition, naming, history and categories of starch noodles; (2) The morphological, physico-chemical, thermal, rheological, characteristics and molecular structure of materials for starch noodles including mung bean starch, pea starch, common bean starch, sweet potato starch, potato starch, corn starch; (3) The traditional and modern processing technology for starch noodles; (4) structure and nutrition of starch noodle; (5) quality evaluation for starch noodles, and (6) quality improvement for starch noodles

In Chapter 5, Li Jun (The Chinese Academy of Agricultural Sciences) and Qian Keying (China Agricultural University) analyzed the recent developments of “Tofu” This chapter including: (1) Definition, Origin, history and Categories, production and consumption of tofu; (2) Material for tofu producing; (3) Processing technology of tofu; (4) Researches and progress on processing, quality and nutrition of tofu

Fan Junfeng (Beijing Forestry University) in Chapter 6, “Sofu (soybean cheese)”

provided analysis of (1) introduction; (2) The classification of sufu; (3) Processing Development in sufu manufacture; (4) Enzymes Produced during Fermentation; (5) The characteristics of sufu and (6) Microbiological aspects of sufu

In Chapter 7, Li Zaigui and Li Dongwen (China Agricultural University) presented a fermentation soybean- “douchi” It consisted from: (1) Introduction; (2) Materials for the production; (3) Processing technology of douchi; (4) Researches on douchi

Finally, in Chapter 8, Lin Qin (Shanghai Institute of Technology), Chou Ju and Jiang Da (China Agricultural University) gave a detailed account on Chinese vinegar including to: (1) Introduction; (2) Raw Materials for vinegar processing; (3) Nutrition and taste of vinegar; (4) Manufacture of Chinese Vinegar; (5) Research and technological advances in vinegar; (6) Quality standards of vinegar in China

Together the chapters presented here provide a wide-ranging conspectus of the variety of traditional Chinese foods

Li Zaigui, with the help of Tan Hongzhuo, edited all of the parts The work of Ms Wang Aili, Ms Li Lu and Ms Yang Hong are also helpful

We believe that “The Production and Research Progress on traditional Chinese food”

make a particularly strong subject of study to increase our understanding of the globalization trend in Chinese foods distribution and consumption While it is recognized that the information contained in this document is far from being exhaustive, as there are many traditional Chinese foods that are not cited in the literature, it is hoped that its publication will encourage nutritionists, food scientists, and food technologists in the region to give this subject more attention and to develop appropriate technologies for the induction and commercial distribution of traditional Chinese foods It also is our sincere hope and expectation that it will serve as an essential reference on the manufacturing of traditional food products, for professionals in government, industry, and academia

In the last part of this introduction, we thank all the contributors for sharing their experience in their fields of expertise They are the people who made this book possible and many references are detailed after each chapter

Dr Li Zaigui and Dr Tan Hongzhuo

Chapter 1

M ANTOU (C HINESE S TEAMED B READ , CSB)

There are two kinds of staple foods in China: wheat and rice The annual production of wheat and rice has been about 100 million tons and 200 million tons in recent years Wheat originated in the Central region, and was introduced to China in the Neolithic Age The inscriptions on the bones and tortoise shells dating from the Shang Dynasty (1751–1122 B.C.) indicated that wheat was already widely grown throughout the Henan province in central China People used stone mortars to grind wheat into flour and made wheaten food by hand

Bing was the common name of cooked wheaten foods in ancient times There was further

development of wheaten foods during the Han Dynasty (206 B.C to 220 A.D.) The writer

Liu Shi reported on shou mian (a kind of fermentation dough) in his work Shi Ming This

indicated that, at that time, dough fermentation technology was already in use The Chinese had mastered flour fermentation techniques by using the easily fermented rice soup as a catalyst Later, bases were used to neutralize the fermentation process when making dough It was said that, during the “Three Kingdoms” (221–263 A.D.), steamed bread was first made and similar products were then introduced to Japan, Korea, and Southeast Asian countries Steamed bread has evolved continuously throughout Chinese history so that today there are many styles of steamed bread

The most common food made from flour would be Mantou, Chinese steamed bread (CSB) Chinese steamed bread, a kind of Chinese traditional fermented food based on wheat flour, has been consumed for at least 2,000 years in China It is a staple food for the Chinese people, especially in northern China where it is eaten at almost every meal and also has been gaining popularity in southern China in recent years Today, the industrialization of CSB production in China has the same trend of development as western-style bread production in western countries Although there are similarities between CSB and western-style bread, the processing of CSB is quite different from that of western-style bread The processing of CSB uses a method that produces a product with a dense crumb and a thin smooth white skin rather than the brown crust of traditional western bread

1 INSTRUCTION

1.1 The Definition of CSB

Chinese steamed bread is a leavened wheat flour product, which is cooked by steaming in

a steamer The most common type of steamed breads, weighing about 100 g, is either round

or roughly cylindrical in shape, white in color, and has a smooth, shiny, surface devoid of a crust The crumb texture varies from dense to open, and the flavor varies to suit local tastes One piece of dough can be used to make different forms of steamed products such as steamed bread, steamed bun, and steamed twisted roll Steamed products can be made with or without

fillings The products without filling are called steamed bread, or mantou (Figure 1-1), and with fillings are called a steamed bun (baozi) Other forms of steamed products include twisted rolls in various shapes (huajuan)

In the national standard of “Chinese steamed bread made of wheat flour” which was issued at the beginning of 2008, CSB was defined as “wheat flour and water as raw material, microzyme as leavening and steamed food” (Sun, 2008) From the definition, baozi with fillings is not CSB and manju in Japan (the character of manju in Japanese is the same as that

of mantou in Chinese) is also not CSB

1.2 Categories of CSB

There are three main styles of steamed bread in China and East, Southeast Asian countries as northern, southern and Guangdong styles The northern style, preferred in northern China, has a very cohesive and elastic eating quality, a higher arch domed shape and dense structure The southern style has a soft, elastic, and medium cohesive eating quality, a lower arch domed shape and open structure The Guangdong style, which is popular in the very southern part of China, and East, Southeast Asian countries, has an open structure, a sweet taste, and a very soft and elastic, but not a cohesive eating quality People usually consume this style of steamed bread as a snack

Figure 1-1 A view of steamed bread making in a small countryside shop

Steamed bread is a staple food in the wheat-growing area of northern China, representing approximately 45% of flour produced in this region In contrast, a lesser proportion is used in the south, where rice and noodles are more popular People in the south often consume CSB for breakfast The dough of CSB for northern- and southern-style steamed bread is made of flour, water, and yeast while for the Guangdong-style steamed bread, up to 25% sugar, 10% fat and 1.2% salt are added

1.3 Consumption of CSB

Wheaten foods have had a very important role in the diet and culture of Asian countries since very early times Today, steamed bread is a common food in China and the East, Southeast Asian regions Millions of people consume it regularly The commercial production

of frozen steamed bread, creating more convenience for consumers, has raised their popularity even further

Over the past two decades, the rapidly growing economies in China and East, Southeast Asian countries have led to an improvement of living standards The demand for convenience and quality of steamed bread is increasing Many innovative products have been developed, particularly among those distributed to supermarket chains Sold both fresh and frozen, an enormous variety of types is available For example, layered steamed breads with chocolate

or taro colorings have been widely marketed Whole meal steamed bread has also recently appeared in markets In addition, there are some new types of steamed breads made from mixtures of wheat flour with other flours such as buckwheat, millet, sorghum, black rice, or maize flour These new products are marketed as health foods and are sold in northern China There is increasing production of steamed bread, buns, and rolls in factories equipped with modern machines

Steamed bread is the most important food in the main growing areas of wheat In Henan Province, for example, steamed bread is the main staple for over 90% of the residents and nearly 100% for county-side residents

About 20 years ago, almost all steamed breads were prepared by hand and in the home, but now 90% of the steamed bread that is sold is prepared by machine in the city while the conditions in the countryside have not been improved much (Sun, 2008) The first automatic production line for steamed bread was established in China at the beginning of 1980, but now, the manufacturers of steamed-bread-making machines could be found all around China

2 MATERIALS FOR THE PRODUCTION OF CSB

The materials for steamed bread making are simply wheat flour, yeast and water while in some cases adding sugar, especially for Guangdong style steamed bread Yeast includes enzyme and traditional starter culture (‘Jiaotou’ in Chinese) Although someone reported the steamed bread was better using Jiaotou than that using enzymes, but Jiaotou is inconvenient and makes it difficult to control the quality of steamed bread so it is just used in homes or in a few small shops

2.1 Wheat Flour

Wheat flour is the most important material for CSB making and accounts for about 60%

of product in weight The effects of wheat flour on the quality of steamed bread are very complex and still not clear even though there were many studies done on the subject It is acceptable that protein, lipid, starch and water are all related with the crystalline network forming during steaming Protein was considered to be the most important factor affecting the quality of steamed bread, but the role of starch in flour has been reconsidered and reaffirmed recently

2.1.1 Carbohydrate Composition

The main composition of flour is carbohydrate It includes starch and non-starch polysaccharides In a modern milling factory, the crude fiber content of flours can be kept so low that only traces of it (under 0.5%) remain in the final product

Starch is present in dough in the native state where it appears as distinct semi-crystalline granules During dough preparation, starch absorbs up to about 46% water It was suggested

to act as inert filler in the continuous protein matrix of the dough, while some researchers described dough as a bicontinuous network of starch and protein Other studies reported that the rheological behavior of wheat dough is influenced by the specific properties of the starch granule surface and by the presence of amylolytic enzymes

Due to the combined effects of heat and moisture during the steaming process, the starch granules gelatinized and swelled However, their granular identity is retained A small amount

of starch (mainly amylose) is leached into the intergranular phase Furthermore, due to phase separation, amylose and amylopectin are not homogeneously distributed in the granules: the centre of the large granules is enriched in amylose, while the outergranule layers are enriched

in amylopectin Part of the solubilised amylose forms inclusion complexes with both added (if any) and endogenous wheat polar lipids, as evidenced by the V crystal type of fresh crumbs

In cereal science, non-starch polysaccharides (NSP) is a generic term for arabinoxylans (AX), β-glucan, cellulose and arabinogalactan-peptides, i.e polysaccharides that differ from amylose and amylopectin either by the nature of their composing monosaccharides and/or by the nature of their linkages Water-extractable arabinoxylans (WE-AX) added to dough increase dough consistency and stiffness and decrease mixing time On the same dough consistency basis, WE-AX addition increases baking absorption but does not affect mixing time, lowers the energy input to achieve optimal mixing and enhances resistance to extension and decreases extensibility WE-AX of high average molecular weight (Mr 201,000–555,000) exerts greater effects on baking absorption and development time than that of lower molecular weight counterparts (Mr 50,000–134,000) Addition of water-unextractable arabinoxylans (WU-AX) has similar effects as that of WE-AX, but does not alter dough extensibility properties A positive correlation between flour WU-AX level and baking absorption was equally shown for endogenous WU-AX through fractionation-reconstitution bread-making experiments Using this approach, extensibility decreased and resistance to extension increased with the increasing of WU-AX content of flour This would feed the hypothesis that the WU-AX rich cell-wall fragments interfere with optimal gluten formation during dough mixing WE-AX functioned somewhat as gluten during fermentation as it slows down the diffusion rate of carbon dioxide out of the dough, thus contributing to gas retention

However, they lack elastic properties Presumably, WE-AX increases dough foam stability

because it increases the viscosity of the dough aqueous phase which in its turn stabilizes the

gas cells liquid films Others attributed the positive impact of WE-AX to the formation of a

secondary, weaker network enforcing the gluten network Upon addition of WU-AX, gas

retention and evolution of dough were similar to those of the control dough This observation

is in contrast to the postulated negative impact of WU-AX which suggests that they: (i)

destabilize gas cells by forming physical barriers for gluten during dough development, (ii)

absorb a large amount of water which consequently is not available for gluten development

and film formation, (iii) perforate the gas cells which causes them to coalesce

It is assumed that, during the initial phase of baking, AX affect bread making by

mechanisms equal to those observed for fermentation Stabilization of gas cells by WE-AX

will prolong the oven rise and improve bread characteristics (crumb firmness, structure and

texture, loaf volume), while WU-AX enhance gas cell coalescence and decrease gas retention,

resulting in poorer bread quality Indeed, fractionation-reconstitution experiments

demonstrated that loaf volume was increased both when decreasing the WU-AX content and

increasing the level of WE-AX of medium and high molecular weight in dough

2.1.2 Protein Composition

It is said that the protein of wheat flour decides the suitability of steamed bread making,

and the medium protein content is most suitable But a wide scope of wheat flour with low,

medium or high protein content are used in steamed bread making in different areas For

example, the soft wheat with wet gluten content 21~24% is the main kind of wheat flour in

Anhui province While the wet gluten content of flour for CSB making may be over 30% in

Shandong province So not only the content but also the character relate to the properties of

water

Non-gluten protein (mainly monomeric)

Metabolic and structural proteins

Variable Globulin Extractable in

dilute salt

Non-gluten protein (mainly monomeric)

Metabolic and structural proteins

Prolamin-type seed storage proteins

Dough viscosity/

Prolamin type seed storage proteins

Dough elasticity/

strength Residue Unextractable Gluten proteins (high

molecular weight polymers) and polymeric non-gluten proteins (triticins)

Prolamin-type (gluten) and lobulin-type (triticin) seed storage proteins

Variable

Suitable protein content of flour is significantly related to the color, structure and smoothness of surface, taste and volume of CSB (Dong et al., 2005) If the dried protein content of flour was over 13%, the surface of CSB would crinkle and the color became gray But if that is lower than 10%, the surface and color of CSB would be smooth and white, but the construction, texture and taste will be affected negatively It is also said that the suitable protein content of flour for southern-style CSB is a little lower than that for northern-style CSB

Osborne introduced a solubility-based classification of plant proteins using sequential extraction in the following series of solvents: (1) water, (2) dilute salt solution, (3) aqueous alcohol and (4) dilute acid or alkali Using this Osborne classification scheme, wheat proteins were classified in albumins, globulins, gliadins and glutenins, respectively (Table 1-1) From

a functional point of view, two groups of wheat proteins should be distinguished: the gluten proteins, with either no role or just a minor role in CSB making, and the gluten proteins, with a major role in CSB making

non-The producing quality of wheat flour is largely determined by its proteins Both quantity and composition (quality) of proteins are important for wheat quality The observation and producing performance of wheat flour is linearly related with its protein content though different linear relationships exist for different wheat varieties Notwithstanding some roles of different non-gluten proteins (e.g., certain enzymes, enzyme inhibitors, lipid-binding proteins and possibly also triticins) in the producing process are observed, the main quality determinant of the producing process is the gluten proteins Indeed, the unusual properties of the gluten proteins allow wheat flour to transform into the dough with suitable properties for production Gluten proteins undergo various changes during the different steps of CSB making, although the nature of these changes, like the native gluten protein structure itself, is poorly understood

The gliadin/glutenin ratio of gluten proteins is very important This is a direct consequence that, within the viscoelastic gluten protein network of dough, gliadin and glutenin showed different roles Due to their large size, glutenin polymers form a continuous network that provides strength (resistance to deformation) and elasticity to the dough On the other hand, the monomeric gliadins are believed to act as plasticizers of the glutenin polymeric system In this way, they provide plasticity/viscosity to wheat flour dough For bread making, an appropriate balance between dough viscosity and elasticity/strength is required Up to a certain limit, higher dough strength increases loaf volume of CSB just as that of western style bread The second factor in gluten protein quality is the quality of its glutenin fraction (extractable as well as unextractable) Though differences in gliadin properties might also have some effects, it is now generally believed that differences in glutenin properties are more important in explaining gluten protein quality during production Although a lot of questions still remain because of the lack of detailed knowledge about the molecular structure of glutenin and its contribution to elasticity, it can be assumed that differences in glutenin functionality during production result from differences in (i) composition, (ii) structure and/or (iii) size distribution of the glutenin polymers (Veraverbeke and Delcou, 2002) (Figure 1-2) Firstly, differences in glutenin composition may result in differences in the non-covalent interactions that determine the elasticity of glutenin Each wheat variety contains 3~5 different high molecular weight glutenin subunits (HMW-GS) and about 7~16 different low molecular weight glutenin subunits (LMW-GS) Knowing that more than 20 different HMW-GS and more than 40 different LMW-GS have been detected so far in

different wheat varieties, explains an enormous variation in glutenin composition between different wheat varieties Secondly, although it is hard to hypothesize on this matter because

of the poor knowledge of the structure of glutenin, it can be assumed that (even subtle) differences in the structure of glutenin largely affect glutenin functionality in bread making

To a certain extent, differences in the structure of glutenin may also result from differences in glutenin composition For example, if the glutenin structure is indeed branched, as suggested from its rheological behavior, GS composition may determine the degree of branching since some GS would allow for branching while others would not Thirdly, based on polymer theories, only the polymers above a certain size would contribute to the elasticity of the glutenin polymer network This corresponds well with several reports in the literature on positive correlations between dough strength/bread making performance and levels of the unextractable/least extractable glutenin fractions and/or the largest glutenin polymers As with the glutenin structure, differences in the glutenin size distribution may also (at least partly) be attributed to differences in GS composition Size differences of GS, resulting in variations in, e.g., HMW-GS/LMW-GS ratio, and/or different numbers of cysteine residues available in GS for cross-linking, influencing, e.g., the ratio of ‘chain terminator’ GS (only one cysteine residue available for cross-linking) to ‘chain extender’ GS (two or more cysteine residues available for cross-linking), may significantly affect glutenin size distribution

Gliadin/glutenin ratio

Gluten protein quality

Gliadin quality

Gluteninquality

Glutenin size distribution

Glutenin structure

Glutenin composition

Figure 1-2 Factors governing CSB making quality and wheat dough rheological properties

During the production process, dramatic changes occur in the gluten proteins that are probably a combination of changes in protein surface hydrophobicity, sulphydryl/disulphide interchanges and formation of new disulphide cross-links As a result of these heat-induced changes as well as those of the starch, the typical foam structure is formed

2.1.3 Lipids

It is well known that flour lipids, in particular the non-starch lipids (NSL) fraction, significantly affect the production quality of CSB Starch lipids are too strongly bound in the starch granules and are essentially unavailable to affect dough processing before starch gelatinization occurs When non-polar wheat lipids are added back to defatted flour, bread loaf volume is reduced This observation has been ascribed to free fatty acids Polar lipids can have a similar detrimental effect, but at higher concentrations, they increase loaf volume In addition, the ratio of non-polar to polar lipids and the galactolipid content of the free NSL are strongly correlated with loaf volume Presumably, lipid functionality is related to their effect

on the stability of the gas cells In this respect, the positive influence of the polar lipids is attributed to their ability to form lipid monolayers at the gas/liquid interphase of the gas cells, thus increasing the gas retention of the dough Furthermore, polar flour lipids positively contribute to dough handling properties as well In addition, during dough mixing, two processes occur which affect the lipids and hence the bread making performance of the flour First, most of the free NSL ‘bind’ to gluten or the starch granule surface and, as a consequence, their extractability is reduced Secondly, polyunsaturated fatty acids are oxidised by wheat lipoxygenase, yielding hydroxyperoxides and free radicals These compounds can oxidise other constituents, such as proteins and carotenoids, thus affecting dough rheological properties and crumb colour

2.1.4 Milling Methods of Flour

Components of flour affect the CSB making properties, while milling methods also have

an obvious influence on the quality of CSB and CSB making properties

We milled 3 kinds of wheat (strong wheat 8901, medium wheat Nanyang White Wheat (NYWW), and weak wheat Australia White Wheat (AWW)) with debranning or conventional milling and investigated the variation in components and properties of CSB making (Sun et al., 2007) As shown in table 1-2, the ash and pericarp contents of most of the samples from debranned flour were higher than that of flour The mean pericarp particle size in the conventional flour was larger than that from debranned flour except for some of the second flour in the extent of debranning about 4.5% Thus a high pericarp and ash content affects the flour quality, and a smaller pericarp size has a negative impact on steamed bread height Fortunately, Debranned flour mixed with water was whiter and brighter compared to conventional flour

The starch damage of the conventional flours was higher than that of debranned flours, moreover the mean particle size of conventional samples were smaller than that of debranned flour

Damaged starch hydrates easily and is more susceptible to enzymatic hydrolysis A certain level of damaged starch is beneficial because of the increase of baking absorption and gassing power of the dough However, excessive starch damage can over-hydrate the dough, accelerate enzymatic action, and lead to inferior baking performance Flour has the best baking performance when the starch damage is between 4.5–8.0%.The results demonstrated

that starch damage decreased markedly in debranned flour The 7% starch damage in all AWW flours is acceptable The starch damage of NYWWD and NYWWD was the lowest, about 4.5% The particle sizes of NYWWD were a little larger than that of NYWWC, but the starch damage of NYWWD was clearly lower The starch damage of 8901C was higher than 8.3%, while for 8901D it was below 7 %

As shown in Figure 1-3, the effects of milling methods on the quality of CSB The quality scores of AWWCII and 8901CII were higher than that of AWWDII and 8901DII However, steamed breads made from debranned second flour, had clearly improved quality scores, volume, volume/weight and structure (height, skin color, skin structure and interior) of NYWWII (Figure 1-4) and 8901 The shape and structures of steamed breads from AWCII and 8901CII were better than that of debranned flour The method of milling did not show a significant effect on the texture of steamed bread, except for the second flour from NYWW Research found that debranning had only slight effects on the quality of top flour in terms

of gluten index, maximum resistance, starch damage, particle size, falling number, flour color and pasting properties The low gluten index (r=-0.66, p<0.05) and large pericarp size of NYWWDII and 8901DII improved the volume of steamed bread and resulted in higher steamed bread quality (r=0.89, p<0.001) and whiter skin color (r=0.624, p<0.05) Hence it can be concluded that debranning improved the quality of second flour from NYWW and

8901, and in addition improved the performance of the flour in steamed bread making

Table 1-2 Flour quality for debranning and conventional flour (Sun et al., 2007)

Name Protein

content

Ash Pericarp

content (%)

Mean Pericarp size

Falling number (s)

Particle size (µm)

Starch damage (%) AWWDI 8.34i 0.61fg 1.54a 0.048d 510b 75.90b 6.83e

AWWDII 9.34h 0.83d 1.54a 0.029f 518b 76.28b 7.25cd AWWCII 9.22h 0.75e 0.97d 0.039e 401d 65.13c 7.44c NYWWDI 11.39g 0.60g 0.88d 0.059c 429d 63.84cd 4.56g NYWWCI 11.26g 0.59g 0.60e 0.038ef 400d 62.38cd 5.86f

D: debranning; C: conventional; I: top flour; II: second flour

Ⅰ 80

D

Ⅰ 68

D

Ⅰ 74

C

Ⅰ 73

C

Ⅰ

Ⅰ 79

D

Ⅱ 68

D

Ⅱ 76

D

Ⅱ 84

C

Ⅱ

Ⅱ 67

C

Ⅱ 74

2.2 Yeast

Yeast cells metabolize fermentable sugars (glucose, fructose, sucrose and maltose) under anaerobic conditions producing carbon dioxideas a waste product, which acts as a leavening agent andenhances dough volume Yeast also supports both glutennetwork and aromatic compounds production.Active cells of yeast are available as a compressed cake or in dried form The compressed cake contains approximately 70% moisture so it is highly perishable unless refrigerated Active dry yeast is produced by extruding cake yeast in fine strands, which are dried to low moisture content Instant yeast is made from more active strains of yeast and dried faster and to a lower level of moisture Although active dry yeast has a long shelf-life at room temperature, it must be hydrated before being incorporated with other ingredients In contrast, instant yeast can be incorporated with flour andother ingredients without prior hydration The actions of yeast may be shown in a simplified form as follows:

2.3 Water

Water is necessary for the formation of dough and is responsible for its fluidity It assists the dispersion of yeast cells and is the medium for food transportation to the yeast through cell membranes Water is also needed for starch and sucrose hydrolysis The water is necessary to activate enzymes that bring on the formation of new bonds between the macromolecules in the flour, and alter the rheological properties of dough The amount of added water is related to the moisture content and the physicochemical properties of the flour The properties of the dough will vary according to the level of added water The dough will

be firm, difficult to mould if the addition of water is not enough and it will result in small volume and poor external appearance of CSB While the dough would be soft, it also would

be difficult to mould if the addition of water exceeded the needed quantity, and resulted in

low quality of CSB The ‘optimum’ level of water is really the maximum quantity we can get into the dough and still be able to mould the pieces and give bread of acceptable quality

3 PROCESSING TECHNOLOGY

Several ingredients can be used for the production of steamed bread, the most important

of which are flour, yeast and water As soon as dough is properly prepared and steamed, a product with superior quality and sensory features could be expected However, fresh production is the one with a short shelf-life and a number of chemical and physical alterations occur during storage, known as staling As a result of these changes, steamed bread quality deteriorates gradually as it loses its freshness quickly compared with western-style bread The pleasant aroma vanishes and the flavor brings out a stale feeling Those preservation problems

in combination with the increasing market demands and the complexity of the traditional procedure, which requires night or early morning labor, led to the evolvement of several technologies in order to improve the preservation of CSB Meanwhile, several additives were introduced in order to increase shelf-life and enhance its quality, conservation, sensory perception or even nutritional value

Fresh CSB making Fermentation

Figure 1-5 Process flow diagram of frozen dough CSB and fresh CSB making

The processing of CSB is almost the same as that of bread The process includes mixing, fermentation, remixing, molding, proofing, steaming, cooling and packing Of course, processing is related significantly with the quality of CSB and there are many researches on the effects

The processes of tradition and frozen CSB are just a little different from each other as shown in Figure 1-5

Over the past few years, the CSB industry has exploited the advantages and applications

of the freezing technology and developed a special interest in it in order to cover its customers (consumers, food service) needs for products with increased shelf-life Frozen dough CSB is expected to be characterized by quick preparation time and affordable price, and look and taste as if they were freshly homemade But the application of frozen dough for Chinese steamed bread making still needs to be studied

3.1 Optimization of Laboratory Processing Procedure of CSB

To evaluate the quality of CSB or improve the processing technology, a laboratory processing procedure of CSB is necessary Some of the steps may be completely mechanized but most of them are still manual work

At first, Huang et al (1993) studied the optimized processing procedure by response surface methodology for northern-style CSB Compressed yeast (4.5 g) was dispersed in a volume of water 20 g less than that of 70% Farinograph water absorption Flour (200 g) was then mixed with the yeast/water slurry (30°C) in a 300 g Farinograph bowl and fermented (32°C, 85% RH) The fermented dough was placed in the mixing bowl, additional flour (100 g) and water (20 g) were added and the dough was remixed and sheeted (20 times) by passing through a pair of rolls (diameter 11 cm; gap, 7.2 mm; and 11 rev/min) After each pass, the dough was folded end-to-end and re-sheeted in a unidirectional manner The dough piece was then divided (100g dough pieces) and gently shaped by hand to form a rounded dough piece with a smooth upper surface The dough piece was placed into an Extensograph rounder (smooth surface facing up), rounded (20 times), placed into a tray, proofed for 20 min and steamed for 20 min In the process, the mixing time is 3/4 of Farinograph dough development time and the remixing time is 1/4 of Farinograph dough development time

Huang et al (1998) also researched the optimization of a laboratory processing procedure for southern-style CSB in 1998 For southern-style CSB, the mixing time and remixing time

is 50% and 180% of Farinograph dough development time, and the fermentation time and the proofing time is 150 min and 35 min, respectively And the amount of flour used for mixing

is 240 g and the additional flour for remixing is 60g

The manual method of CSB is also shown in a National Standard of the People’s Republic of China named as wheat varieties for specific end-uses (China State Bureau of Technical Supervision, R.P China, 1998, GB/T 17320-1998B) The formula consisted of 100

g flour, 1 g instant active dry yeast The instant active dry yeast was dissolved in different volumes of water The volume of water was determined through experiments (about 80% of water absorption capacity of Farinograph) The ingredients were put into an aluminum basin orderly, kneaded by hand until optimum dough consistency appeared After resting for 15 min

at room temperature, the dough was molded into a near hemisphere-like shape with a height

of 60 mm on a smooth surface Then the dough was kneaded by hand again for 3 min and

proofed for about 60 min in an incubator at 33 ºC and 85% RH After that, the dough was shaped and put into a steamer with boiling water, and steamed for 20 min

But manual methods can only be used in some parts of the countryside or in research Most of CSB are processed by a mechanized method especially in the city so the effects of the mechanized method and the relationship between the quality of material and product focusing on the northern-style CSB will be introduced

a continuous protein phase that, in fully developed dough, surrounds the starch granules The chemical bonds that stabilize gluten proteins in dough are covalent and secondary bonds The covalent bonds are disulfide bonds, which form inter- and intramolecular crossbonds in the proteins during dough formation by the sulfide-disulfide interchange The secondary bonds are hydrogen, hydrophilic, hydrophobic, and ionic bonds and polar interactions

The mixers are divided by the design of the beater arms in the chamber The two main variations are based on roller bars and an elliptical-shaped beater In both cases the mixing action is strongly influenced by the relatively small size of the gap between the outer edge of the beaters and the sides of the bowl The main action tends to be one of stretching and folding of the dough The dough is picked up by the mixer blades and thrown against the outer side of the bowl

In order to get suitable CSB dough, there are some things to which producers should pay more attention Firstly, the amount of flour added into the mixer should be definite

Secondly, it is generally considered more desirable to start with drier dough and adding water as you work to complete the kneading process This is because flour does not absorb water (hydrate) quickly But professional producers are experienced at knowing how much water to add By adding water in two phases, the dough may be mixed inadequately In order

to obtain a desirable structure of dough, flour should be mixed with the required amount of water When the amount of water added is relatively less, the transformation of starch into gelatin may be incomplete As a result, CSB could easily dry and scrapes At the same time, the CSB will become stale quicker On the contrary, when excess water is used, it is not entirely constrained during starch gelatinization and a certain amount of water is still in free statement which makes crumbs moist and sticky The water-holding capacity of flour depends

on its type, origin and other properties Zhang (2005) investigated the effects of addition of water on the quality of CSB As shown in table 1-3, addition of water had negative effects on the height, appearance and whiteness of CSB but is good to skin, inner structure and volume

in a suitable range

Chen et al (2005) also researched the effect of water addition on the CSB processing They adjusted the addition of water according to FWA values of six cultivars of wheat flour

as table 1-5 and had the relationship between water addition and CSB quality as table 1-5 and

1-6 In table 1-5 and table 1-6, strong wheat was Gaocheng 8901 and Zhengmai 9023,

medium wheat included Zhongyou 9507 and Ningchun 4, while weak wheat included Jing

411 and Jingdong 8

They indicated that the effects of water addition were different from the strong, medium

and weak wheat For example, the effects for medium flours were not so obvious, but

increasing of water addition for strong flours almost improved the total quality, and even

decreased the total quality for weak flours (table 1-6)

To same flours, the addition of water for southern-style CSB must be larger than that of

northern-style CSB The addition of water in dough for CSB is lower than that of western

bread making by 20–35%, hence dough for CSB making is stiffer and firmer than the dough

for western bread making

Thirdly, the mixing time is decided by flour characteristics and mixing speed Mixing

should be quick, homogenous and temperature controlled Lower mixing speed required a

longer mixing time in order to develop the gluten structure for strong flours Dough is

kneaded after the initial mixing to realign the strands of gluten and form the network structure

of the dough Dough kneaded properly is shiny and elastic If a little piece is pulled off,

considerable extensibility will be observed If dough was still undermixed, starch and proteins

would be distributed unevenly, and compact protein masses are stretched out into sheets

during mixing When dough is overmixed, gluten proteins become stressed, few disulfide

bonds would be broken to form thiyl radicals and gluten proteins are partially depolimerized,

resulting in a greater solubility and less extractability of lipids Overmixing usually results in

sticky dough, partly because mechanical forces applied to the dough decreased the molecular

weight of the protein Prolonged mixing can enhance the effects of oxidants on disaggregation

of large protein aggregates, probably because of oxidation of more -SH groups

Lastly, the mixing environment including RH and temperature should be determinate

Table 1-3.The effects of addition of water on the quality of CSB (Zhang, 2005)

Ratio of added

water(water/flour,w/w)

Skin Inner structure

Height Appearance Volume Whiteness

Table 1-4 Additional water for 6 samples at five WA levels (Chen et al., 2005)

Table 1-5 Correlation coefficients between water addition and CSB quality

(Chen et al., 2005)

Water addition Parameter

Weight 0.957** 0.904** 0.983** Width 0.881** 0.929** 0.905** Height 0.928** 0.744** 0.927**

were identified as Bacillus cereus, Brevibacillus brevis, Acinetobacter twoffii The source of

Bacillus cereus, Brevibacillus brevis, Acinetobacter twoffii in Jiaotou was assumed to be

casual contamination from the environment The species of isolated yeasts were identified as Saccharomyces cerevisiae, which was widely used in brewing and genetics research Carbohydrates were fermented by yeasts to produce carbon dioxide and a little ethanol The

carbon dioxide formed gas bubbles which contributed to the interior structure of CSB, similar

to the interior structure of bread Ding et al (2007) reported that the pH value changed during dough fermentation by Jiaotou During fermentation, the pH value remained in the first 3 hours From 3 to 6 hours, the pH value decreased gradually from 5.7 to 5.5 In the last 2 hours, the value decreased sharply to 4.9 The LAB and yeast counts changed in the last 2 hours were the reason for the observed pH value decrease Despite the relatively low level of LAB in the fermented dough by Jiaotou, these organisms were likely to be significant in flavor development in CSB After 5 hr fermentation, the pH gradually declined, especially for the last 2 hr, while the yeast counts remained un-fluctuated, other than the increase in the preceding 5 hr This reduction in pH value as a result of the organic acids production by LAB and yeasts was almost likely to have reflected the cause of suppression of yeast population in the dough

The starter produces the product that is high in acidity, giving it a distinct tang This ferment sits at room temperature, to ferment and develop flavor until it is used to make the rest of the dough Long fermentation develops extra gluten strength for the dough, adds depth and complexity of flavor, and increases the shelf-life of products There are several different types of pre-ferments, which vary mainly by the amount of water they contain For CSB, the way to prepare Jiaotou is to save a small piece of dough from one batch to add at the end of mixing the dough (during the last couple of minutes, since the structure is already developed) Jiaotou used to keep for more than 24 hr under a comfortable temperature and RH But the disadvantage is the producing condition and values of pH of Jiaotou are difficult to control so experience is heavily needed

pre-In recent years, commercial dry yeast products were used instead of Jiaotou for the industrial production of CSB Fermentation is what happens when yeast comes in contact with the flour and water Then the carbon dioxide is held in by a network of gluten strands, or protein, formed by kneading together the flour and water, and it leavens or causes the products to rise Temperature control is a very important factor in fermentation Yeast is active at temperatures around 30°C At warmer temperatures, the yeast is more active and grows and multiplies more quickly The fermentation process itself produces heat When fermentation takes place at too high a temperature, unpleasant flavors are produced Length of fermentation is another important factor that determines both the flavor and the texture of products If the dough ferments for too long, the yeast and bacteria will consume all of the sugar in the flour Compared with Jiaotou, the advantages of commercial yeast products would include more rapid dough fermentation, less acid produced and purer flavor The overall procedure involves mixing all of the ingredients and then allowing the dough to ferment for several hours

Compared to Jiaotou, commercial yeast had a shorter dough fermentation time (usually

no more than 2 hr), while the pH value of dough could be kept almost unchangeable during the fermentation But CSB processed with yeast is short in fermentation flavor and has poor re-steaming ability compared with that of Jiaotou Although the quality of steamed bread is still acceptable, the process lacks flexibility and is sensitive to time In other words, the dough must be steamed soon after fermentation Otherwise, prolonged fermentation will result in the forming of excess air cells and weaken the structure of the CSB

Table 1-6 The quality of CSB made from different flours at five water addition levels (Chen et al., 2005)

Sample WA Weight Volume Width Height SV SR SC CC SH SM ST SR TS

70% 98.4c 232.5b 8.8b 6.0a 9.5b 7.3a 4.4a 3.4a 4.3a 5.8c 5.1d 23.0b 62.6c 75% 99.6c 260.0ab 8.8b 5.9ab 12.7ab 5.0ab 4.0ab 3.0ab 4.1a 6.5bc 6.9c 32.0a 74.2ab 80% 102.1b 283.8a 8.8b 5.7bc 14.8a 3.0bc 3.4b 2.5b 4.3a 7.5ab 7.8b 33.5a 76.8ab 85% 103.8b 291.3a 9.1ab 5.6cd 15.2a 1.5bc 3.9ab 2.8ab 4.3a 8.1a 8.7a 34.0a 78.4a Strong

90% 105.8a 291.3a 9.4a 5.5d 14.5a 0.0c 4.4a 2.8ab 4.3a 8.0a 7.6bc 30.0a 71.5b 70% 95.9c 237.5c 8.5d 5.7a 11.0b 5.0a 3.6a 1.6a 4.1a 6.4b 6.8a 23.0b 61.5b 75% 97.3c 242.5c 8.6cd 5.6ab 11.2b 3.5ab 3.5a 2.1a 4.0a 7.0b 7.2a 26.0b 64.5b 80% 99.4b 252.5c 8.9bc 5.5ab 11.8b 1.5bc 3.1a 1.9a 4.3a 8.5a 7.9a 30.3a 69.1a 85% 101.8a 272.5b 9.0b 5.4ab 13.5ab 1.0bc 3.4a 1.6a 4.1a 7.8ab 8.2a 25.3b 64.8b Medium

90% 105.3a 291.3a 9.5a 5.4a 14.8a 0.0c 2.8a 1.9a 3.9a 7.5ab 6.8a 19.5c 57.0c 70% 94.6d 230.0b 8.1c 5.8a 10.4a 9.0a 2.5a 0.9a 5.0a 8.8a 8.8a 31.0a 76.3a 75% 96.1c 233.8b 8.5bc 5.7a 10.4a 5.5b 2.3a 0.8a 5.0a 8.5a 8.8a 31.5a 72.8a 80% 97.6c 248.8ab 8.6b 5.5ab 11.9a 2.0c 1.6a 0.6a 5.0a 7.8a 6.0b 29.5a 64.4b 85% 100.0b 260.0a 8.8b 5.4b 12.5a 1.0c 2.0a 0.4a 4.4a 7.8a 6.1b 26.8b 60.9bc Weak

90% 103.2a 267.5a 9.3a 5.1b 12.5a 0.5c 1.6a 0.3a 3.9b 6.5b 6.2b 24.5c 55.9c

Notes: WA=water addition (% farinograph water absorption,), SV=specific volume, SR=spread ratio, SC=skin color, CC=crumb color, SH=shininess, SM=Smoothness, ST=Structure, SR=Stress Relaxation, TS=Total Score The values followed by a different letter are significantly different at 5% probability level

Now, a new method called “remixed fermentation” is widely used in the processing for industrial production There is the sponge and dough method where mixing of ingredients is performed in two steps The leavening agent is prepared during the first step Yeast, flour and water are mixed together The mixture is left to develop for a few hours and, afterwards, it is mixed with the rest of the ingredients In this case, only part of the ingredients are fermented, the sponge Sponge fermentation times may vary considerably, as their composition does The key features of sponge and dough processes are: First, the two-stage process in which part of the total quantity of flour, water and yeast are mixed to form homogeneous soft dough that is called sponge Secondly, the resting of the sponge is formed, in bulk for a prescribed time, mainly depending on flavour requirements Thirdly, the sponge is mixed with the remainder

of the ingredients to form homogeneous dough Lastly, the final dough is processed immediately, although a short period of bulk fermentation may be given The sponge contributes to flavor modification and the development of the final dough The process of flavour development in the sponge, though complex, is observed as an increase in the acidic flavour notes arising from the fermentation by added yeast and other microorganisms naturally present in the flour To maintain the right flavour profile in the finished product, the sponge fermentation conditions are closely controlled to avoid unwanted flavours During the sponge fermentation period, there will be a decrease in pH value with increasing fermentation Under these conditions, the rheological character of the gluten formed during initial sponge mixing changes and the sponge becomes soft and loses much of its elasticity The low pH of the sponge and its unique rheological characters are carried through to the dough where they have the effect of producing a softer and more extensible gluten network after the second mixing In many cases, the addition of sponge changes the rheological character of the final dough sufficiently so that dividing and moulding can proceed without further delay

Ding et al (2007) also compared the quality between Jiaotou fermented CSB and commercial yeast fermented CSB by sensory analysis and a texture analyzer In the sensory evaluation, the interior structure of Jiaotou fermented CSB was superior to that of the commercial ones As to the cohesiveness, the Jiaotou fermented CSB was also superior to the commercial ones There were no significant differences in stickiness between the two kinds of CSB The special flavour was formed during dough fermentation by the microorganisms from the starter culture Jiaotou The results of the texture analyzer test illustrated that the hardness, gumminess and chewiness of Jiaotou fermented CSB were significantly higher than the

commercial ones (p<0.05) The springiness of Jiaotou fermented CSB was lower than that of

commercial CSB, but not significantly different The springiness of the texture analyzer was similar to elasticity by sensory analysis

Even though Jiaotou may contribute to the quality of CSB, the difficulty in controlling the process and the much longer time needed for the processing are the biggest problems of mechanized processing of CSB So the Jiaotou is seldom seen in the CSB industry

Fermentation time is significantly related with the activity of yeast and is variable The suitable temperature and relative humidity for fermentation of CSB dough are 30~35 °C and 70~85% respectively

3.4 Rounding and Molding

Dough is divided into pieces with certain weight and is molded to obtain a desirable shape Dividing and molding modify the structure of gas cells as they induce the coalescence

of small cells into larger ones and contribute as well to the final development of the gluten network After dividing, the dough pieces are commonly worked in some way to change their shape before proof The most common shaping is by rounding The action of mechanical first molding places the dough under stress and strain which may lead to damage of existing gas bubble structure in the dough A portion of the gas is also lost during the dividing and rounding steps Thus, not only does the dough have a chance to rest, but the fermentation also continues, adding a bit more gas into the dough The dough pieces are delivered into a molding system that first sheets the dough between rollers then rolls the dough into the desired final form

The most common equipment for the CSB molding is called lying CSB molder It has parallel rollers The sets of parallel rolls round dough pieces passed through at high speed Sheeting reduces the thickness of the dough pieces The gap between successive pairs of rolls decreases and on leaving the last gap, the dough piece has an ellipsoid shape The other equipment is the plate CSB molder The dough is squeezed and chipped, then rounded on a plate The whiteness of CSB rounded by the plate molder is worse than that of a lying molder

So the application of lying ones is more common Turntable or screw model molders have also been developed recently Figure 1-6 is a scheme of screw model molder of CSB which is widely used for its high efficiency

In regard to frozen CSB, the dough shape is influential on its stability and final quality Round pieces are considered less satisfactory than slabs or cylinders Furthermore, excessive molding can cause heat generation and enhance fermentation prior to freezing

Figure 1-6 Scheme of a screw model molder of CSB

3.5 Proofing

Proofing is mainly attributed to the action of yeast, which contributes many changes in the dough maturing or ripening Properly matured dough exhibits optimum rheological properties (optimum balance of extensibility and elasticity) as well as good machinability and

is necessary to process CSB with a desirable volume During dough maturing, several reactions occur As the yeast is fermented, alcohol and carbon dioxide are produced Because alcohol is water-miscible, appreciable amounts of alcohol influence the colloidal nature of the flour proteins and alter the interfacial tension within the dough Additionally, carbon dioxide dissolves partly in the aqueous phase of the dough and forms weakly ionizable carbonic acid, which lowers the pH of the system Carbon dioxide production also contributes to dough distension which depends on the situation of gas cells Growth of gas cells depends in part on cell size Greater pressure is needed to expand a small gas cell than a larger one, and it is possible that the smallest bubbles will not expand at all Gas cell stabilization and gas retention are of considerable interest as they fairly determine structure and volume of CSB For frozen dough CSB, thawed dough pieces should be left to proof before being steamed, just like the fresh ones, either for a certain period of time or until they obtain the desirable volume In the case of frozen fermented dough, gas cell structure significantly affects frozen storage stability A dough that contains a large number of small bubbles with a narrow size distribution and thick walls will be more stable than a dough that contains bubbles with less uniform size distribution and thin walls surrounding the larger bubbles Proof time for frozen-thawed dough is necessarily longer than that for conventional dough This is due to the lower dough temperature at which thawed pieces reach the proof box, and

to a certain loss of dough gas retention power and yeast activity caused by the freezing process

Figure 1-7 Mechanized steaming line of CSB

3.6 Steaming

Steaming is the last and more impressive part of the CSB making procedure It results in

a series of physical, chemical and biochemical changes, which include volume expansion, evaporation of water, formation of a porous structure, denaturation of protein, gelatinization

of starch and so on The microstructure of flour is continuously modified during all these processes until the structure of the final product is fixed These changes are dependent on the temperature, humidity and duration The role of steaming is to alter the sensory properties of foods, to improve palatability and to extend the range of tastes, aromas and textures in foods produced from raw materials Steaming also destroys enzymes and microorganisms though recontamination of cereal products may occur after The flavor is mainly formed during fermentation and steaming During fermentation, a number of alcohols are formed, including ethanol, isoamyl, amyl alcohols and isobutyl alcohol However, much of these alcohols are lost to environmental space during steaming A large number of organic acids are also formed and several carbonyl compounds have been identified in CSB, which are believed to be important flavor components

CSB had been steamed in bamboo container just as shown in Figure 1-1 and now stainless steel mechanized line (Figure 1-7) is used in large CSB maker

3.7 Cooling and Packaging

Once out of the steamer, the steamed bread is susceptible to microbial spoilage Therefore, cooling must be performed under conditions in which exposure to airborne microorganisms, particularly mold spores, is minimized The CSB also must be cooled enough so that condensate will not form inside the package, a situation that could also lead to microbial problems Various cooling systems are used, including tunnel-type conveyers in which slightly cool air passes counter-current to the direction of the bread, as well as forced air, rack-type coolers

Packaging materials and shapes vary according to products specifications Materials usually applied to frozen dough products are plastic (films, membranes, etc.) and aluminum

In any case, packaging must form an effective, functional barrier to contamination and have sufficient impact and compressive strength to withstand the stresses which it is likely to meet

It must perform satisfactorily in storage and transport This requires good crush resistance, resistance to variable moisture conditions, no embrittlement at the low temperatures experienced by frozen foods, and sufficient scuff resistance to avoid deterioration of the surface appearance of printed matter When designed for frozen dough, it must perform a number of functions, such as contain, protect, identify, and merchandize the food A good packaging material must keep loss of moisture to a minimum Films to be used for frozen dough should posses the following characteristics: good moisture protection, good oxygen-barrier characteristics, physical strength against brittleness and breakage at low temperature, stiffness to work on automatic machinery, and good heat seal-ability

3.8 Freezing

Frozen dough CSB needs more processing procedures such as freezing and thawing in different steps Meanwhile, freezing may have negative effects on the activity of yeast and the quality of CSB These will be explained concisely

Dough pieces, immediately or after a short fermentation period, are frozen and then stored at appropriate temperature Freezing technology can be categorized as mechanical (blast, plate, spiral, impingent, immersion, belt or fluidized bed freezers) and cryogenic Selecting implemented technology based commonly on product requirements and availability

or cost Freezing, as a method of preservation and extension of a food product shelf-life, involves mainly two intimate processes First, temperature reduction and second, phase transition from liquid to solid Freezing normally starts at -1 to -3°C and as the temperature drops most of the water in CSB becomes frozen

3.10 Minimizing Freezing Damage

The quality of frozen dough products is influenced by dough formulation, as well as processing parameters such as dough mixing time, freezing rate, storage duration and thawing rate It appears that these factors may act either independently or synergistically to reduce yeast activity which results in reduced CO2 production or damage to the gluten network, gradual loss of dough strength, declined retention of CO2 and poor CSB making performance The resulting loss of dough strength can be attributed, firstly, to the release of disulphide reducing substances from dead yeast cells, and secondly, to the disruption of the gluten network by ice crystals Yeast cryoresistance is strongly influenced by fermentation time prior to freezing, dough freezing and thawing rates, storage time and temperature fluctuations

of frozen dough

Yeast characteristics also play an important role in determining yeast viability and product quality Yeast content should be higher than in conventional CSB making in order to overcome the prospective loss of activity during freezing, storage and proofing Several ways

to minimize the effect of freezing on dough are reported in literature such as the formation

and use of yeast strains more resistant to freezing, the modification of the CSB making process or the introduction of suitable additives and ingredients for frozen dough

Use of oxidizing agents, whether from natural or chemical origin, exerts an improving effect on dough rheology and on the overall quality of the finished product An oxidant exhibits improving effect by increasing the loaf volume during the first few minutes of steaming Surface-active and dough strengthening agents such as sodium stearoyl lactylate (SSL) or diacetyl tartaric acid esters (DATEM) of mono and diglycerides are also used to maintain loaf volume and crumb softness for frozen dough Medium to strong flour is required for frozen dough production Shortening addition can be within the range of 4–6% of the flour weight Accumulation of less water in the formula has been recommended Reduced water content limits free water in dough during freezing This may constrain ice crystal formation and lessen its negative effects on the quality of frozen dough Ice crystallization particularly affects proteins, lowering the gas retention properties of dough

Mixing duration and dough temperature are important factors in frozen dough stability Gluten network should be fully developed during mixing In frozen dough production, dough temperature after mixing is normally lower, in the range between 19 and 22 °C This modification should be made in order to minimize yeast activity before freezing Dough resting is often avoided completely in frozen dough production to minimize fermentation before freezing though it is a needed procedure for convenience CSB making However, some researchers consider short rest times (8-15 min) to be beneficial Another factor that may affect frozen dough product quality is the influence of storage time and conditions on gluten structure The structure of the gluten protein matrix appears to be disrupted during extended storage resulting in a weakening of dough strength properties, loss of gas retention properties and deterioration of product quality Finally, of great importance on dough rheology and yeast activity are also temperature fluctuations during storage Accurate control of storage temperature, rapid movement of products between stores and correct stock rotation and control can minimize these fluctuations

4 REQUIREMENTS OF FLOUR QUALITY FOR DIFFERENT KINDS OF CSB

Wheat flour is the main component of CSB and the quality of flour greatly affects the properties of CSB making It is generally said that medium flours are suitable to CSB making considering the content and properties of flour, but things may be more complex

In fact, the minor wheat flour constituents such as ash, lipid, enzymes and non-starch polysaccharides also play a comparatively important role in the CSB making process There are many researches focused on the relationship between the quality of flour and CSB and they have continued to increase in recent years as shown in Table 1-7

Table 1-7 Researches on the quality of flours and CSB since 2000

Quality Properties of Steamed Bread and White Salted Noodle of Commercial Wheat Flour in Xinjiang

Acta Agriculturae Occidentalis Sinica, 2008(3):91-96

Rheological Properties of Dough and Quality

of Mantou

Journal of Henan University of Technology(Natural (Science Edition), 2008(02):2-7

Using Wheat Flour of Xiaoyan 22

Journal of Triticeae Crops, 2008(01):61-65

Zhang Jingmei, Li

Feng

Discuss Importance which the North-east Agriculture and Reclamation Wheat Reasonably Match

Grain Processing 2008(01):27-29

of flour on the CSB quality

Grain Processing 2007(05):19-22 Shen Jiong;

Wang Xuedong;

Li Qinglong

Relationship between the Components of Wheat Flour and Quality of Chinese Steamed Bread

Journal of Wuhan Polytechnic University

2007(01):19-22

French Wheat and its Application in Chinese Flour Foods

Grain Processing

2006(09):9-11

Chinese Steamed Bread Quality

Food Science

2005(12): 57-61 Zhang Zhao;

and cooking properties

Journal of Hygiene Research

2003(01):75-77

Characters of Wheat and Processing Quality of Flour Food

Xinjiang Agricultural Sciences 2002(05):290-292

Xinjiang Agricultural Sciences 2002(04):220-221

for Making Chinese Steamed Bread

Journal of Zhengzhou Grain College 2002,23(04):38-42

quality and their food quality

Journal of Northwest Sci-Tech University of Agriculture and Forestry 2001(05):61-63

in China

Review of China Agricultural Science and Technology 2000(03):62-68

Northern Style Chinese Steamed Bread

JOURNAL OF THE CHINESE CEREALS AND OILS ASSOCIATION 2000,15(02):10-15

4.1 Requirement of Flour Quality for Northern-Style Steamed Bread

The textures and taste of northern-style CSB are much different from that of style CSB, so the requirements on wheat cultivars and flour quality are different, too

southern-Huang et al (1996) studied the relationships between flour quality and steamed bread quality for 49 kinds of Australian and Chinese wheat The result is summarized in Table 1-8 Protein content was significant correlated with specific volume score and spread ratio score Both skin and crumb color scores were negatively correlated with flour color grade and ash content, but were positively correlated with dough strength It was also observed that the longer the dough had to be mixed, the whiter the skin and the crumb became Smoothness of CSB did not correlate well with flour quality and appeared to be more dependent on processing procedures There was no significant linear correlation between protein content and total score of CSB However, when protein content was below 10%, it was linearly and positively correlated with the total score of steamed bread As protein content increased further (i.e over 10%), the total score was not significantly influenced by protein content and was more dependent on other flour quality attributes Overall, it was apparent that dough strength was more important than protein content in determining quality of steamed bread Most parameters for dough strength (Farinograph dough development time, stability, mixing tolerance, Extensograph maximum resistance and extensibility) were significantly correlated with individual components of steamed bread quality It was therefore clear that dough strength was a significant determinant of northern style steam bread quality It contributed positively to steamed bread quality in terms of specific volume, skin and crumb color, structure and eating quality Extensograph maximum resistance exhibited the highest correlation with total score of steamed bead All RVA parameters (except peak time) of flour were positively correlated with specific volume Flour peak viscosity showed the best correlation with specific volume, crumb structure and total score A positive correlation was also observed between eating quality and flour peak viscosity Other starch-related parameters, including starch damage, starch granule size distribution, maltose figure and falling number, showed minor correlations with steamed bread quality attributes

Zhu et al (2001) investigated the effects of flour protein content and composition of HMW glutenin subunits, using several kinds of Chinese and Australian wheat as samples, on northern style CSB quality The results indicated that at high protein level, the Australian wheat cultivar, with the biotype processing HMW glutenin subunits 5+10, had a significantly higher total score than the biotype with subunits 2+12 However, no significant difference existed between the two biotypes at the low protein lever The improvement of CSB quality with 5+10 biotype could be due to its higher protein content However, a significant difference still existed even though the protein contents of samples with 5+10 and 2+12 biotypes were all at same high level, suggesting that there is other factor that could affect CSB quality One explanation might be the difference of size distribution of glutenin polymers between the flours with these glutenin subunits

Table 1-8 Correlation between flour quality and steamed bread quality attributes

from 49 kinds of wheat samples (Huang et al., 1996)

Specific

volume

Spread ratio score

Skin color score

Crumb color score

Shininess score

Smoothness score

Structure Eating

quality score

Total score Protein 0.49 *** -0.73 *** N.S N.S -0.36 * N.S N.S N.S N.S Ash N.S -0.39 ** -0.54 *** -0.54 *** N.S -0.32 * -0.30 * N.S -0.45 **

number

N.S 0.42 ** N.S N.S N.S N.S N.S N.S N.S

4.2 Requirements of Flour Quality for Southern-style CSB

Southern-style CSB is somewhat softer and whiter than northern-style CSB The flour made from medium or soft wheat may be suitable to the preparing of southern-style CSB Fifty Australian and seven Chinese wheat flours were used to investigate the requirements of flour quality for southern-style CSB (Huang et al 1996) Both protein quantity and quality were identified as major determinants for specific volume of steamed bread Protein content had a more significant effect on the specific volume of this kind of steamed bread than that for northern-style ones Dough strength showed an important role in determining the overall quality of steamed bread, but was not so significant effect as to that for northern style External smoothness and protein content of southern-style CSB showed significant negative correlation, of the same for smoothness and flour dough strength

Flour with medium protein content and dough strength, medium or high falling number, and low ash content was recommended for the producing of southern-style CSB No significant correlation was found between flour RVA viscosity parameters and steamed bread quality

4.3 Requirements Flour Quality for Guangdong-style CSB

The majority of Guangdong–style CSB is prepared with flour and sugar Preferences in sweetness, cohesiveness, and structure range throughout different regions and countries There are few reports about flour quality requirements of this kind of CSB Flour quality

specifications from several modern mills in Hong Kong, Shenzhen, and Guangzhou where the CSB of this kind was consumed mainly indicated that flours with a protein content of 7.5-9.0%, wet gluten of 19-22%, and ash of 0.45-0.55% is used for this product So low protein content and ash may be requested for flour of Guangdong-style CSB so that the CSB becomes whiter and softer

4.4 Requirements of Flour Quality for Manual Process or Mechanized

Process

Almost all of CSB were processed manually in about 20 years ago, but now, most of it is processed mechanically in city although the condition is different at all Usually, stronger flour is desired for mechanized process while softer flour is suitable to for manual process The different requirements of flour are mainly resulted from the different mixing strength If the flour is too soft, the gluten of dough could not endure the mechanized mixing during dough preparing If the flour is too strong, mixing will be difficult and dough quality may be uneven for manual process

Research showed the qualities of CSB prepared by manual or mechanized methods with same kinds of wheat flour were different He et al (2003) selected 56 Chinese cultivars from major wheat growing areas, including North China Plain, Yellow and Huai Valley, Yangtze Region Besides, there were 10 Australian cultivars grown in Anyang located in Yellow and Huai Valleys and Chengdu located in Yangtze region The mechanized method was from Huang et al (1993), also Manual method is according to SB/T 10139-93 The cultivars from North China Plain possess slightly poorer CSB quality using manual method, while Australian cultivars perform slightly better than Chinese cultivars from all ecological zones with both manual and mechanized methods in Anyang It is observed that Australian cultivars showed much better CSB quality (total score) than Chinese cultivars in Chengdu with both manual and mechanized methods This may be due partly to the strong gluten and good sprouting tolerance (as indicated by falling number and RVA peak viscosity) of Australian cultivars Chinese wheat is well known for its rather weak gluten type In addition, not enough selection pressure for sprouting tolerance is applied in wheat breeding programs since quality became an important trait only recently These results indicate that selection for strong gluten and good sprouting tolerance could improve the CSB quality for wheat from Chengdu and other southern China locations, despite the unfavorable environmental effects on CSB quality The correlation coefficient between flour quality and CSB quality differed with bread making method (manual or mechanized) For example, protein content, dough strength parameters such as SDS sedimentation value, water absorption, development time, stability, extensibility, resistance, and extension showed positive correlations with loaf volume and elasticity under both manual and mechanized conditions, however, they showed significantly negative association with appearance and stickiness under manual conditions, and very small negative or even positive association with appearance and stickiness under mechanized conditions The correlation coefficients between appearance and protein content, development time, stability, and extension area are –0.29, –0.62, –0.44, and –0.50 under manual conditions, and are –0.18, –0.21, –0.03, and –0.07 under mechanized conditions, respectively This indicates that high protein content and good gluten quality will contribute positively to the improvement of loaf volume and elasticity regardless of processing methods, but they